Journal of Neuro-Ophthalmology, June 1991, Volume 11, Issue 2

Chronic isolated trochlear nerve palsy produced by intracavernous internal carotid artery aneurysm. Report of a case.

The fourth cranial nerve is rarely affected by intracranial aneurysms, and when this occurs other motor ocular nerves and the trigeminal nerve are almost always involved as well. In the case reported, a middle-aged woman presented with a long-standing selective and stationary palsy of the right superior oblique muscle. Neuroradiologic studies disclosed an aneurysm arising at the C-3 segment of the right internal carotid artery.

Journal of Clinical Nel/ Yo- ophthalmology 11( 2): 104- 108, 1991. © 1991 Raven Press, Ltd., New York Chronic Isolated Trochlear Nerve Palsy Produced by Intracavernous Internal Carotid Artery Aneurysm Report of a Case Jorge Arruga, M. D., Pilar De Rivas, M. D., Hernan L. Espinet, M. D., and Gerardo Conesa, M. D. The fourth cranial nerve is rarely affected by intracranial aneurysms, and when this occurs other motor ocular nerves and the trigeminal nerve are almost always in­volved as well. In the case reported, a middle- aged woman presented with a long- standing selective and stationary palsy of the right superior oblique muscle. Neuroradiologic studies disclosed an aneurysm arising at the C- 3 segment of the right internal carotid artery. Key Words: Carotid aneurysms- Cavernous sinus­Trochlear nerve- Trochlear palsy. From the Departments of Ophthalmology ( J. A., P. D. R.), Neuroradiology ( H. L. E.), and Neurosurgery ( G. c.), Hospital de Bellvitge " Princeps d'Espanya," Barcelona, Spain. Address correspondence and reprint requests to Dr. Jorge Arruga at Servicio de Oftalmologia, Hospital de Bellvitge " Prin­ceps d'Espanya," Feixa Llarga sin, 08907 L'Hospitalet del Llo­bregat, Barcelona, Spain. 104 The relationship between trochlear nerve palsies and intracranial aneurysms has seldom been estab­lished. We report a case in which an unremitting paresis of the fourth cranial nerve occurred in as­sociation with an aneurysm of the ipsilateral inter­nal carotid artery in its intracavernous portion. CASE REPORT Mrs. A. A. R., a 45- year- old woman, was referred to our hospital in May 1989 for evaluation of dou­ble vision. Her past medical history was irrelevant, but 2 years before referral she started complaining of painless vertical diplopia on gaze to the left; this had remained stabilized since then. On examina­tion, visual acuity was 20/ 20 RE and 20/ 20 LE with normal color vision and visual fields au. Pupillary size and reflexes and ophthalmoscopic exam showed no abnormalities. Ocular motility testing disclosed a right hypertropia of 8 prism diopters in the left field of gaze above, straight, and below ( Fig. 1), and the Hess- Lancaster test confirmed an underacting right superior oblique with an over­acting right inferior oblique ( Fig. 2). Amplitude of vertical fusion was not increased and the review of old photographs did not reveal torticollis. There was no ptosis or clinical signs of orbital disease: the fifth and seventh nerves were unaffected and the remainder of the neurological examination was un­remarkable. Blood pressure was 130/ 60 mmHg, and SMA, hemogram and ESR gave normal re­sults. Cerebral magnetic resonance imaging was then performed; it showed a rounded structure with a voiding signal that projected upwards from the right parasellar area, displacing the optic nerve and compressing the gyrus rectus on this side ( Fig. 3). A right carotid angiogram showed the lesion to TROCHLEAR PALSY DUE TO ANEURYSM 105 FIG. 1. Examination of ocular versions in nine positions of gaze. Note hypertropia of the RE in up- left, straight- left, and down- left positions, as well as orthotropia in the remainder positions. be an aneurysm originating from the C- 3 segment of the internal carotid artery ( Fig. 4). Because the aneurysm extended into the subarachnoid space, neurosurgical treatment of the lesion was consid­ered, but the patient refused operation. Therefore, she was subjected to regular clinical and neurora­diologic follow- up and her condition has remained unchanged for 1V2 years. DISCUSSION Acquired palsies of the trochlear nerve are most commonly attributed to head trauma, microvascu­lar disease ( diabetes, hypertension), or decompen­sation of congenital paresis ( 1- 10) ( see also Table 1). Other less common causes are neoplasms, in­tracranial surgery, herpes zoster, infections, colla­gen vascular disease, or multiple sclerosis. In some instances the etiology remains undetermined. In fact, tumors that affect the trochlear nerve almost always produce associated neurological signs ( 4,7,11). Therefore, in nontraumatic cases our work- up on adult patients ( 11) initially includes determination of blood pressure, general blood screening, and a glucose tolerance test, as well as research for signs of congenital decompensated paresis. The majority of these nontraumatic fourth nerve palsies recover spontaneously within a few months ( 5- 8) [ 85% of our cases]. Only when there is a history of previous malignancy, or associated neurological signs develop, or the palsy does not improve after 4- 6 months, do we perform neuro­radiologic studies including cerebral computed to­mography scan, MRI and angiography. Our patient presented with a 2- year history of diplopia. On examination, a long- standing palsy of U. E U. D FIG. 2. Hess- lancaster chart shows an underaction of the superior oblique muscle with an overaction of the ipsilat­eral antagonist inferior oblique muscle in the RE. I Clin Neuro- ophthalmol. Vol. II, No. 2, 1991 106 J. ARRUGA ET AL. A B FIG. 3. Short TR and short TE magnetic resonance images. Axial section: the aneu­rysm ( black arrow) projects upward through a wide diaphragma sellae ( A); Coronal section: the aneurysm ( small arrow) causes compression of the gyrus rectus ( black arrow heads) on the right side ( B). The right optic nerve is displaced outwards ( white arrowhead). Note the normal position of the left optic nerve ( open arrow). TABLE 1. Causes of acquired trochlear nerve palsy in our hospital ( 84 cases) the right trochlear nerve with secondary contrac­ture of the ipsilateral inferior oblique muscle was diagnosed. Neuroradiologic techniques revealed a right intracavernous carotid aneurysm presumably involving the fourth cranial nerve. In the different series published about trochlear palsies there are only five cases of intracranial aneurysms being the implicated cause, representing less than 1% of all the cases ( Table 2). In two of the five cases, the palsy occurred in the course of subarachnoid bleeding ( 4,8), whereas two others were associated with nonruptured aneurysms located at the poste­rior cerebral artery ( 5) and at the basilar artery ( 8). TABLE 2. Aneurysms as a cause of trochlear palsy according to different authors The third case of Rush and Younge's series ( 8), together with the case published by Maurice­Williams and Harvey ( 12) are, to our knowledge, the only two reports in the literature of isolated fourth nerve palsies attributed to direct involve­ment from carotid aneurysms within the cavern­ous sinus. Conversely, in the classic series of in­tracavernous aneurysms causing ophthalmoplegia ( 13- 16), the fourth nerve is always affected in as­sociation with the sixth and/ or the third nerves. In a more recent series ( 17), trochlear palsy is said to Aneurysms ( cases) Trochlear palsies Etiology Cases Percentage Author ( ref. no.) ( cases) Microvascular Traumatisms Congenital decompensated Postsurgery Inflammations Cerebrovascular accident Anesthesia Aneurysm Arteriovenous malformation Metastatic tumor Undetermined Total 31 26 93 3 2 1 1 1 1 6 84 37 31 11 4 4 2 1 1 1 1 7 100 Rucker ( 1) Rucker ( 2) Khawam ( 3) Burger ( 4) Rougier ( 5) Younge ( 6) Coppeto ( 7) Rush ( 8) von Noorden ( 9) Trimble ( 10) Arruga ( present study) Total 67 84 40 33 40 52 43 172 270 54 84 939 o oo11o o3o o1 6 I Clin NeurCH'phllullmol, Vol. 11, No. 2, 1991 TROCHLEAR PALSY DUE TO ANEURYSM 107 A B FIG. 4. Right carotid angiography. Lateral CA) and oblique ( 8) projections. The aneu­rysm originates at the C- 3 portion of the right internal carotid artery ( arrow). Occur with 16% of these lesions, but information is lacking about simultaneous involvement of other cranial nerves in such cases. The long- term course of ocular motility distur­bances produced by intracavernous aneurysms is either progressive, stationary, or regressive, al­though some degree of motor deficit persists as a rule ( 13- 16). However, there are a few cases in which a complete recovery of the ophthalmoplegia has occurred spontaneously ( 18). Regarding evo- I Clin Neuro- ophthalmol, Vol. 11, No. 2, 1991 108 f. ARRUGA ET AL. lution in the reported cases of isolated trochlear nerve palsies, Rush and Younge's patient had an expanding intracavernous aneurysm, and the palsy eventually progressed to total ophthalmople­gia ( 8); whereas Maurice- Williams and Harvey's patient had a small aneurysm posteriorly located in the sinus, and the palsy regressed completely after 6 months ( 12). Our case had a stationary course during the period that we followed her. Studies on the pathogenesis of ocular motor pal­sies produced by intracranial aneurysms ( 19) have demonstrated, in cases without subarachnoid bleeding, two main mechanisms of involvement: ( a) dilatation of the aneurysmal sac with mechan­ical stretching of the nerves and ( b) aneurysm leak­age with intraneural hemorrhage. Alternatively, acute ischemia from occlusion of the vessels that supply the nerves as a result of either compression or thrombosis has also been advocated ( 20). In this regard, the clinical course of both Rush and Younge's case ( 8) and our case suggest direct nerve compression as the underlying mechanism. By contrast, in Maurice- Williams and Harvey's case ( 12) the prompt recovery of the palsy leaves as the only possible explanation transient ischemia, ei­ther consecutive to or concomitant with the aneu­rysmal lesion. Concerning selective trochlear in­volvement, it is known that with intracavernous aneurysms this nerve lies in contact with the me­dial and superior walls of the enlarging sac ( 21). In our case the upward growth of the sac may be responsible for the isolated compression with re­sulting ipsilateral superior oblique muscle weak­ness. Otherwise, although cranial nerves show a high capability of functional adjustment in re­sponse to gradual compression from these lesions ( 19), it is possible that some unusual anatomical factor such as the location of the fourth nerve within the deep layer of the lateral wall of the cav­ernous sinus ( 22) may account for its selective dys­function. In conclusion, aneurysms are very rare causes of isolated trochlear nerve palsy. However, this pos­sibility should be considered in chronic nonremit­ting cases, even in the absence of progression or of additional neurological signs. 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